1. Field of the Invention
The present invention relates to an optical spot generation device for writing and reading data to and from a recording medium such as an optical disc and an optical card, and more particularly to an optical spot generation device for a recording medium capable of being made compact.
2. Description of the Related Art
With an optical spot generation device for writing and reading data to and from a recording medium such as an optical disc and an optical card, collimated light is formed by a collimator lens and passed through an objective lens to apply an optical spot on a target track of a recording medium. In order to apply an optical spot on a target track of a recording medium, the objective lens is controlled through tracking serve to move it in a direction perpendicular to the track.
The collimator lens has a size which allows the objective lens to receive the collimated light on the whole surface of the objective lens, irrespective of the position of the objective lens in its motion range. From this reason, a conventional collimator lens is circular.
Since a conventional collimator lens is circular, its diameter is set so that the objective lens can receive the collimated light from the collimator lens on the whole surface of the objective lens, irrespective of the position of the objective lens in its motion range along the direction perpendicular to the track.
It is an object of the present invention to provide an optical spot generation device for a recording medium capable of being made compact.
According to an optical spot generation device for a recording medium of this invention, a light converging optical element receives light from a collimator and forms an optical spot on a track of the recording medium, the optical spot being displaced in a direction perpendicular to the track during tracking servo. In the optical spot generation device for a recording medium, the collimator has a size which allows the light converging optical element to receive collimated light from the collimator on a whole surface of the light converging optical element, irrespective of a position of the light converging optical element in its motion range. A length of the collimator in a track direction is cut shorter than a length in the direction perpendicular to the track, by an amount corresponding to that the light converging optical element is displaced in the direction perpendicular to the track and is not displaced in the track direction.
The collimator may be a collimator lens, an aspheric press lens, a lens with its aspheric surface being formed with a replica, a lens having a refractivity distribution in an optical axis direction, a lens with a refractivity distribution in a radial direction, a lens made of glass spherically polished lenses having different refractivities and attached together, and a lens made of a Fresnel zone plate.
This optical spot generation device is applied not only to a read only optical pickup device but also to a read/write optical spot generation device and a write only optical spot generation device. In writing data to a recording medium, the power of a laser output is made lager than in reading data from the recording medium. A light beam applied from the collimator to the light converging optical element is not limited only to one beam, but two or more beams may be used. The spot (M, E, F, G, H, I, J) on a recording medium may be a single spot or a plurality of spots.
The length of the collimator in the track direction can be made shorter than that in the direction perpendicular to the track, by an amount corresponding to that the objective lens is not displaced in the track lens.
In the optical spot generation device for a recording medium of this invention, a mirror is provided for changing an optical axis direction of an output optical axis thereof by 90xc2x0 from an input optical axis thereof, wherein the collimator is disposed between the mirror and the light converging optical element on the output optical axis, a side of the cut portion of the collimator abuts on a surface of the mirror, and the collimator is mounted partially superposed upon the mirror along the optical axis direction.
The collimator with its opposite ends being cut along the track direction has its side of the cut portion being abutted on the surface of the mirror and the collimator is mounted partially superposed upon the mirror along the output optical axis direction. Accordingly, the length in the output optical axis of the optical spot generation device for a recording medium can be shortened.
In the optical spot generation device for a recording medium of this invention, a mirror is provided for changing an optical axis direction of an output optical axis thereof by 90xc2x0 from an input optical axis thereof, wherein the collimator is disposed on the input optical axis, with the track direction of the collimator being set in parallel to direction of the output optical axis.
The collimator is disposed on the input optical axis, with the track direction or shorter length direction thereof being set in parallel to the direction of the output optical axis. Accordingly, the height of the optical spot generation device in the region of the input optical axis of the mirror can be lowered.